The present invention relates to a device for angle measurement and to a corresponding method.
The demand for high-precision yet also robust angle measuring systems in the automobile industry is constantly rising. At present, the areas in which angle measuring systems are used include an electronic stability program (ESP) and electrically assisted steering systems. Over the long term, the transition to steer-by-wire will increase the demand for angle measuring systems still further, and this development involves a simultaneous increase in the accuracy demanded.
Magnetic sensors are predestined for use in the automobile, because of their contactless, robust measurement principle. If an angle measuring system realized with magnetic sensors is based on scanning a transducer wheel that is either itself magnetized or comprising ferromagnetic material and on moving past the scanning sensor distorts the field of a transducer magnet, production tolerances limit the accuracy of the system. Aspects that are especially problematic are eccentricities, polarization or tooth pitch errors, and nonhomogeneities in the field amplitudes. Moreover, the scanning sensors cannot be positioned arbitrarily accurately, so that additional positioning tolerances are also involved.
Conventional methods for angle measurement are known for instance from German Patent Disclosure DE-P 195 34 995. German Patent Disclosure DE-P 199 58 598.9, which had not yet been published by the filing date of the present application, for instance describes a Nonius method, in which magnetic multipole wheels, each with a different number of pole pairs, are used, and the sensor signals obtained from suitably disposed sensors are evaluated. Once again, however, angle errors are caused by the aforementioned tolerances.